Disc-shaped tools called disc milling cutters are generally used for slot cutting.
FIG. 1 shows an example of the disc milling cutters. The disc milling cutter 1 with a diameter D includes cartridges 2 used as cutting edges along the outer circumference of the disc milling cutter 1. The disc milling cutter 1 cuts a desired slot 4 on a workpiece 3 by circumferentially rotating. If the diameter D of the disc milling cutter 1 is larger, the vibration of the disc milling cutter 1 during slot cutting is larger. This possibly leads to a breakage of the cutting parts and a deterioration of accuracy of slot cutting.
FIGS. 2 and 3 show examples of one of the vibration modes of the disc milling cutter 1 during slot cutting. FIGS. 2 and 3 show results of mode analysis on a disc milling cutter 1 with a diameter D of 1200 mm by the finite element method. In the analysis, the disc milling cutter 1 was fixed to a shaft 5. As shown in FIGS. 2 and 3, the vibration modes of the disc milling cutter 1 cause an outer peripheral portion of the disc milling cutter 1 to undulate in the z-axis direction (along the shaft 5). For example, in a vibration mode at a frequency of 267 Hz (FIG. 2) where the vibration amplitude in the z-axis direction is maximized, four nodes are generated along the outer circumference of the disc milling cutter 1. In a vibration mode at a frequency of 374 Hz (FIG. 3), six nodes are generated along the outer circumference of the disc milling cutter 1.
Thus, it is known that the dominant vibration of the disc milling cutter 1 is in a mode in which an outer circumference of the disc milling cutter 1 undulates in the z-axis direction.
Examples of existing techniques for cutting workpiece using disc-shaped tools are disclosed in JP 2011-194564 and JP 2012-196729.
JP 2011-194564 discloses a face milling cutter for rotary cutting which includes a rotation axis and a cutter body. The cutter body includes, in an end portion thereof, plural insert seats on which rotary cutting inserts are placed. The face milling cutter is positioned on the inside of the cutter body and includes plural damping elements for damping vibration of the face milling cutter. The damping elements extend in parallel with the rotation axis to be adjacent to one end of the cutter body while radially shifted away from the rotation axis.
JP 2012-196729 discloses a rotary cutting tool which has cutting edges attached to a disc-like cutter body. An annular groove is formed on a surface of the cutter body. A ring-shaped weight is placed in the groove via viscoelastic bodies such that the weight can move relative to the cutter body in the axial direction of the cutter body.
In the face milling cutter disclosed in JP 2011-194564, the vibration of the face milling cutter is damped by the plural damping elements included in the cutter body. However, JP 2011-194564 fails to disclose details of the structure of the damping elements. If a vibration mode to be damped differs from the vibration mode of the face milling cutter in JP 2011-194564, the face milling cutter may vibrate in a direction in which the damping elements are not effective, that is, the vibration of the face milling cutter cannot be damped. Therefore, the technique disclosed in JP 2011-194564 cannot be used as it is.
In JP 2012-196729, a vibration damping structure and a rotary cutting tool are disclosed. The vibration damping structure is intended for a vibration mode occurring when cutting force is generated in diametrical and rotation-axis directions of the tool. However, the vibration damping structure disclosed in JP 2012-196729 is effective only for vibration modes in which the tool displacement by vibration occurs only in one cutting part and in which the tool vibrates in a direction of deflection with respect to she rotation axis of the tool. Therefore, the technique disclosed in JP 2012-196729 cannot be applied to vibration modes of disc-shaped tools in which plural nodes are generated in cutting parts.
The present invention has been made in view of the above problems. An object of the present invention is to provide a side milling cutter for slot cutting whose vibration can be damped even in cases where a vibration mode of the cutter generates plural nodes in a cutting part.